Sunday, June 5, 2011

About 10 years ago, I bought a 1978 John Deere 316 tractor. In reality it is a 300 series, not to be confused with the later model 316's. But for one year, 1978, John Deere renamed their 16 hp 300 series a 316. It is a hardworking tractor, and it shows, see below. The red seat is a boat seat. Much cheaper than a replacement John Deere seat, and it is comfortable. It also has the virtue of having a seat-back which folds flat. That has come in handy on numerous occasions.

Way back in 1978, it looked like this 300:

This tractor has proven to be exceptionally reliable and rugged, and has made me into a loyal John Deere fan. I find it remarkable that I can walk into my local dealer and they will have parts for my 33 year old tractor in stock. Another reason I hang onto this tractor is that it has big tractor features like hydraulic fittings for accessories and individual rear brakes. The plow has both hydraulic lift and angle pistons, and they are powerful. The plow can be lowered to the point that it lifts the front of the tractor clear off the ground.

The angling piston is equally powerful, and I've gotten out of many a jam by using the plow's hydraulics to lift and push the tractor free. Try doing that with the plow on a modern small tractor.
We get plenty of snow, and the little John Deere can handle most of it. Of course there are times when it is outmatched, see below.

This is the road in front of our house. I had to give up at this point and and return home. I was trying to reach my neighbor's house, the red one on the right. I did get my driveway clear, however. But it was another day before I could actually go anywhere!

However, even a John Deere will show some wear after 33 years, and I recently discovered that the front support for the mower deck, called a mule hitch, was badly worn.

The mule hitch has two pulleys that turn the mower drive belt 90 degrees from vertical where it attaches to the front PTO to the horizontal pulley on the mower deck. In spite of all this twisting and turning, the design is reliable and the current belt is now 8 years old.

Years of vibration and the added stress of mowing rough pastures have taken their toll: The hollow pulley support shaft was nearly worn through, and the hole it rides in enlarged.

I designed repair parts that create new bearing surfaces on unworn parts of the shaft, and also solve the problem of the over-sized holes. It is impossible to completely disassemble the mule hitch because the pulley arm was welded on after assembly. Therefore, I had to make one of my parts with a slot instead of a hole. It is OK however, because all of the force, and the wear, is towards the bottom of the slot. A complicated 2 piece part is unnecessary.

I installed my parts with 1/4"-28 high strength cap screws into holes that were tapped 90% of the way through. This made the screws extremely tight, and it is highly unlikely they will vibrate loose.
That was important for I had to mill some of the heads down for clearance. They looks like rivets now, and are just as tight.
Note the amount of space visible in the over-sized hole, and remember that the shaft is worn an equal amount. That added up to about 1/4" of slop, and considerable misalignment of the shaft. The other side of the hitch was worn in the opposite direction, adding to the angular misalignment of the shaft.

The reassembled hitch. One of the screw heads that was milled down is visible to the left of the pulley shaft.
Since the outer portion of the shaft moves only when adjusting the belt, it appears that vibration, and not rotational movement, is the source of the wear. That theory is backed up by the pattern seen in the close up of the shaft. Rotational movement would wear such a pattern smooth. Therefore, I made my parts with a tight fit. There is some friction, but importantly, no free play which would allow vibration to hammer the parts against each other.

Next problem. The hole for the spring tensioner guide rod was nearly worn through! The original hole was at the right. In addition, the guide rod itself was badly worn.

I realized that this wear was due to an error in the design which resulted in considerable side loads on the guide rod. The piece of metal seen above was welded at an angle that guaranteed that the spring and rod would create excessive forces on the left side of the hole. Compounding things was the placement of the bracket. It is off axis from the ideal location by about 15 degrees. While it works, and has worked for 33 years, it could be better. Therefore I made a new spring retainer which is both better located, and better aligned to remove side forces from the guide rod.

This strange looking part is the new spring retainer. The force of the spring wedges it into place, and the screw is there only for insurance.

It has a pocket for the spring which holds it straight and prevents it from walking. This, combined with the improved location reduce side forces to nearly zero. The forces are so low that I did not replace the worn guide rod, as additional wear is unlikely.

A picture of the assembled spring tensioner.

While the rod exits at an angle relative to the retainer, the spring pocket on the opposite side is milled at this angle, and that is what is important.
There is about 1/4" of clearance between the rod and the tractor frame, which is more than enough.
Please note: The spring is quite powerful and under a lot of compression. Use care when working on it!

The pulleys are once again straight, and the overhauled mule hitch should last at least as long as the original, if not longer.

While working on the tractor, I discovered a broken motor mount. I immediately called my local John Deere dealer, and they had mounts in stock! As I previously mentioned, great product support has made me a John Deere fan. I expect everyday parts to be readily available, but rarely replaced parts like motor mounts? That's impressive.

I fixed a few other things while I was at it. The carburetor throttle shaft was also worn, and the engine would no longer idle smoothly or shut off without "dieseling". The ball on the end of the throttle shaft was worn so much that the linkage would fall off. Fortunately, the carburetor has a recess at the top that made it easy to press in a brass bushing, which now supports the shaft on an unworn spot. I cut off the worn ball and replaced it. The engine now idles smoothly, and shuts down properly. If you are experiencing these problems, pay close attention to excess free play of the throttle shaft. It does not take much! I you can feel sideways play in your shaft, you probably have too much. The majority of my wear was on the shaft itself, and not the holes in the carb. It is likely that you could simply purchase a new throttle shaft from John Deere and not have to do what I did.

Finally, the front roller on the mower deck was

also badly worn, as was the shaft it rides on. I made a new shaft, and epoxied brass bushings into the roller. I also added nylon thrust washers and a spacer made from a bored out piece of 1/2" pipe to eliminate side to side play.

The first run of the tractor after the repairs was a resounding success. The engine starts readily, even at idle setting. It runs smoothly, and no longer shakes excessively, thanks to the new motor mount. The mower deck appeared to run better, easily cutting through the tall grass that had grown while I was making my repairs. It compares favorably to much newer tractors, and is surprisingly economical. The massive single cylinder cast iron Kohler engine burns only 3/4 of a gallon an hour while cutting grass. That is less than a gallon an acre. It runs 6.5 hours on a full tank. Another advantage is that this tractor uses a full size car battery, not a little lawn tractor battery, which has typically lasted me maybe 3 years. I'm still using the Pep Boys battery the previous owner installed 10 years ago!
Unfortunately for John Deere, I may be a fan, but I don't expect to be replacing my tractor anytime soon.

Update: I removed my deck and put it away for the season. My overhauled hitch now has two seasons of use, and while it is dirty, there is no wear on the repaired parts. The shaft is as tight as when I made the repair.

If you install a plow with a hydraulic angle piston, that piston is connected to the same hydraulic lines as the deck lift piston. For the angle piston to work properly, the deck piston has to be immobilized. I have seen this done by putting a manual valve on the inlet line to the lift piston. When using the plow, the operator reaches under the tractor and closes the valve. I find this to be an overly complicated fix to a simple problem. Here is my solution. I took a piece of steel and drilled two holes in it 14 1/2 inches apart. One hole is 1/2 inch and the other is 3/8 inch. Put the half inch hole in the mower deck attach point, and use a 3/8 inch bolt to attach the steel bar to the 3/8 inch hole in the deck lift shaft. Your deck height knob must be screwed all the way down, as seen here.
The piston now cannot move more than 1/8 of an inch. Much easier and cheaper than the hydraulic valve idea.